Pluggable fiber optic transceiver modules having form factors with names such as Xenpak, X2, XFP and SFP use receptacles to connect the optical subassemblies with optical fiber cables for optical signal transmission into and out of the transceiver. To align the connector of the optical fiber with the fiber stub inside the receptacle for better optical signal transmission, two styles of centering bores are usually used: solid and split-sleeve. We refer to these types of centering bores as solid sleeves and split sleeves, respectively. These centering bores are configured to have a fiber stub at one longitudinal side, and a ferrule with an optical fiber attached thereto at the other side.
An example of such a solid sleeve is shown in FIG. 1. The solid bore sleeve 101 is completely rotationally symmetrical and constructed of a rigid ceramic material, typically Zirconia. Due to fabrication tolerances the diameter of the solid sleeve can not be made exact, or at the very least, it is difficult to do so. Therefore, the inner diameter of the sleeve 101 must be made slightly larger than the outer diameter of the connector ferrule to be inserted (not shown). This gap can be up to 2 μm.
This configuration is not able to give a very stable and repeatable optical connection for the optical fiber connector with the fiber stub 102, because the connector ferrule can move with the sleeve such that the center of the optical fiber in the ferrule may become off center with respect to the center of the fiber in the optical stub 102. This “offset” changes the light power transmitted, causing degraded performance and potential errors.
A split sleeve bore 201 as shown in FIG. 2, in contrast, is separated lengthwise along the cylindrical wall by a slot 202, and is made with an inner diameter slightly smaller than the diameter of the connector ferrule. This split sleeve structure is more flexible and is therefore able to enlarge its inner diameter slightly to accommodate the diameters of the fiber stub and ferrule. When the ferrule (not show) is inserted, the split sleeve can expand and then clamp down on the inserted ferrule, thereby accurately centering the connector ferrule with the fiber stub inside the receptacle.
However, when a side load is applied to connector ferrule, the split sleeve can expand and thereby allow a large tilt or even an offset of the connector ferrule which will cause a misalignment between the two fiber cores and hence induce optical power variations in the connection. Essentially, to achieve the improved ability of the split sleeve over the solid sleeve, one must sacrifice the overall stability of the sleeve itself.
One prior art solution to the above problem is a stepped split sleeve. A stepped split sleeve has a variable wall thickness along the length thereof. Using a stepped thickness, the thicker end of the split sleeve bore is able to hold the fiber stub tightly and therefore the expansion of split sleeve only occurs at the thinner end of the bore. In this way, the amount of connector tilt inside the split sleeve bore can be effectively reduced. However, a stepped split sleeve is more difficult to fabricate and hence becomes more expensive than a regular split sleeve bore. Moreover, the stepped sleeve thickness can cause mechanical stress to concentrate around the step area when the split sleeve expands which can cause the split sleeve to crack.
Another method involves press fitting the split sleeve to the fiber stub to tightly couple it and decrease movement. However, mechanical stress can build up around the area where the split sleeve is tightly coupled to the fiber stub, thereby causing the ceramic material to crack. Moreover, press fitting a split sleeve together with fiber stub into the receptacle metal body requires extreme tolerance control of three parts, thereby increasing the cost of the assembly.
Other prior art methods exist, but all fail to provide an economical manner in which to obtain optimum alignment between the ferrule and the fiber stub. It is this issue to which the present invention is largely directed.